Some polymer compounds exhibit a phenomenon of phase transition by responding to the external stimulus such as heat, pH, or light, and the development of a temperature sensor, a separation membrane, an adsorbent, a drug releasing agent, a water absorbent, a water retention agent, a humidity controlling agent, and an agent for indicator which apply the phase transition phenomenon has been actively carried out.
Among the polymer compounds as described above, compounds which exhibit a phase transition phenomenon by responding to heat are referred to as a temperature responsive polymer, and a living polymer of vinyl ether containing an oxyethylene chain is known as such a polymer. This living polymer exhibits hydrophilicity at a temperature equal to or lower than a specific temperature, and hydrophobicity at a temperature exceeding the specific temperature. Because it is an oily compound, the polymer is not equipped with moldability and film-forming properties, and thus the use thereof is greatly limited.
As a means for solving such a problem, the introduction of an azo group into a temperature responsive polymer has been investigated. For example, there has been an investigation as to imparting the temperature responsiveness associated with hydrophilicity and hydrophobicity to various general-purpose resin films by conducting the surface modification thereof using a diblock copolymer of vinyl ether containing an oxyethylene chain and vinyl ether containing an azobenzene structure (Patent Literature 1 and Non Patent Literature 1).
In addition, a specific star-shaped vinyl ether polymer having a polyvinyl ether chain as the arm portion is also regarded to exhibit temperature responsiveness (Patent Literature 2).